A Rankine cycle (RC) can capture a portion of heat energy that normally would be wasted (“waste heat”) and convert a portion of that captured heat energy into energy that can perform useful work or into some other form of energy. Systems utilizing an RC are sometimes called waste heat recovery (WHR) systems. For example, heat from an internal combustion engine system such as exhaust gas heat energy and other engine heat sources (e.g., engine oil, exhaust gas, charge gas, water jackets) can be captured and converted to useful energy (e.g., electrical or mechanical energy). In this way, a portion of the waste heat energy can be recovered to increase the efficiency of a system including one or more waste heat sources.
FIG. 1 shows an exemplary RC system 1 including a feed pump 10, a recuperator 12, a boiler/superheater (heat exchanger) 14, an energy conversion device 16 (e.g., expander, turbine etc.), a condenser 18, and a receiver 20. The path of the RC through and between these elements contains a working fluid that the feed pump 10 moves along the path and provides as a high pressure liquid to the recuperator 12 and heat exchanger 14. The recuperator 12 is a heat exchanger that increases the thermal efficiency of the RC by transferring heat to the working fluid along a first path, and at a different point of the RC along a second path, transfers heat from the working fluid. In the first path through the recuperator 12 from the pump 10 to the boiler/superheater 14, heat stored in the recuperator is transferred to the lower temperature working fluid, and the pre-heated working fluid next enters an inlet of the boiler/superheater 14. In the boiler/superheater 14, heat from a waste heat source associated with an internal combustion engine (not shown) (e.g., exhaust gases, engine water jackets, intake air, charge air, engine oil etc.) is transferred to the high pressure working fluid, which causes the working fluid to boil and produces a high pressure vapor that exits the boiler/superheater 14 and enters an inlet of the energy conversion device. While FIG. 1 shows only a single boiler/superheater 14, more than one heat exchanger can be supplied in parallel or in series to more than one heat source associated with the engine.
The pressure and temperature of the working fluid vapor drop as the fluid moves across the energy conversion device, such as a turbine, to produce work. For example, the RC system 1 can include turbine as the energy conversion device 16 that rotates as a result of the expanding working fluid vapor. The turbine can, in turn, cause rotation of an electric generator (not shown). The electric power generated by the generator can be fed into a driveline motor generator (DMG) via power electronics (not shown). A turbine can be configured to alternatively or additionally drive some mechanical element to produce mechanical power. The additional converted energy can be transferred to the engine crankshaft mechanically or electrically, or used to power parasitics and/or storage batteries. Alternatively, the energy conversion device can be adapted to transfer energy from the RC system 1 to another system (e.g., to transfer heat energy from the RC system 1 to a fluid for a heating system). The gases exit the outlet of the energy conversion device, for example, expanded gases exiting the outlet of the turbine 16, and are then cooled and condensed via a condenser 18, which is cooled by a low temperature source (LTS) cooling medium, for example, a liquid cooling loop (circuit) including a condenser cooler having RAM airflow and condenser cooler pump (not shown) to move the cooling medium (e.g., glycol, water etc.) in the cooling loop, although other condenser cooling schemes can be employed such as a direct air-cooled heat exchanger.
The expanded working fluid vapors and liquid exiting the outlet of the turbine 16 is provided along the second path through the recuperator 12, where heat is transferred from the working fluid to be stored in the recuperator 12 before entering the condenser 18. The condenser 18 contains one or more passageways though which the working fluid vapors and liquid moves that are cooled by a cooling medium, such as a coolant or air, to cool and condense the working fluid vapors and liquid. The condensed working fluid is provided as a liquid to a receiver vessel 20 where it accumulates before moving to the feed pump 10 to complete the cycle.
The RC working fluid can be a non-organic or an organic working fluid. Some examples of working fluid are Genetron™ R-245fa from Honeywell, Therminol™, Dowtherm J from the Dow Chemical Co., Fluorinol, Toluene, dodecane, isododecane, methylundecane, neopentane, neopentane, octane, water/methanol mixtures, or steam.